For a complete Data Loss Prevention Test you should use HTTP Post Test and HTTPS Post Test. This page allows you to complete a HTTP Post Test and this form is setup to go nowhere. If your Data Loss Prevention software has the ability to block traffic this post action can be blocked.
If this page loaded with SSL, here is a redirect URL http://dlptest.com/http-post/ or just remove the S.
What is a HTTP Post?
A HTTP POST is a request method supported by the HTTP protocol. By design, the POST request method requests that a web server accept the data enclosed in the body of the request message, most likely for storing it. It is often used when uploading a file or when submitting a completed web form. Here at dlptest.com we don’t store any info from the HTTP Post but most websites will store your data.
More info can be found on good old wikipedia